Hydrogen shows great promise for a main energy amid concerns over depletion of fossil fuels and a growing awareness of the importance of environmental preservation. Generation of hydrogen directly by sunlight using a photocatalyst shows promise for a technology with an extremely small effect on the environment.
For example, Patent Document 1 discloses a device and a method for generating hydrogen using a photocatalyst. The document is characterized in supporting a photocatalyst layer on the surface of an electrically conductive layer of a laminate and providing platinum and/or transition metal oxide on the rear surface.
Furthermore, an electrolysis equipment described in Patent Document 2 has a structure in which an anode electrode is arranged above and a cathode electrode is arranged below. The electrolysis equipment does not have a function to separate hydrogen and chlorine, and is configured to have depressions in the lower side of the cathode electrode and to collect hydrogen generated at the depressions.
FIG. 1 is a general view of a conventional device having a structure provided with a photocatalyst electrode and carrying out water electrolysis by irradiation with light. A device of this kind is disclosed in Non-patent Document 1. In the device, an n-type titanium oxide (TiO2) electrode and a platinum (Pt) electrode are immersed in an electrolytic solution in a reservoir, separated by salt bridge of an ion exchange membrane and connected by means of a conducting wire. When the light having a wavelength shorter than 410 nm is irradiated on the TiO2 surface, a photocurrent flows through the wire, so that oxygen is generated on the TiO2 surface and hydrogen is generated on the Pt surface. Oxygen is formed into oxygen gas bubbles and collected at an oxygen gas containing unit. Hydrogen is formed into hydrogen gas bubbles and collected at a hydrogen gas containing unit. The reaction formula by this photocatalyst is represented by the following formulae 101 to 103 with e− and h+ respectively as an electron and a hole produced by photoexcitation. Formula 103 is the sum of Formulae 101 and 102.2h++H2O→(½)O2+2H+(on TiO2)  (Formula 101)2e−+2H+→H2 (on Pt)  (Formula 102)H2O2hν→H2+(½)O2  (Formula 103)
Patent Document 3 and Non-patent Document 2 will be described below.